QGIS and Generic Tools

By Nicolas Baghdadi, Clément Mallet and Mehrez Zribi

These four volumes present innovative thematic applications implemented using the open source software QGIS. These are applications that use remote sensing over continental surfaces. The volumes detail applications of remote sensing over continental surfaces, with a first one discussing applications for agriculture. A second one presents applications for forest, a third presents applications for the continental hydrology, and finally the last volume details applications for environment and risk issues.

• Language: English
• Publisher: Wiley
• Release date: Jan 19, 2018
• ISBN: 9781119490975

Nicolas Baghdadi

Nicolas Baghdadi is Research Director at IRSTEA in France. He is currently the scientific director of the French Land Data Centre (Theia).

Book preview

Introduction

This series, QGIS in Remote Sensing, aims to facilitate the appropriation and operational use of Quantum Geographic Information System (QGIS) software for the specific field of remote sensing. QGIS is an open-source and cross-platform software (Windows, Android, BSD, Linux, Mac OS X, Unix) that has been rapidly developed and steadily adopted over the last 10 years. Thanks to a growing international community of programmers, both in terms of fundamental tools and thematic applications, QGIS is increasingly used with strong and continuous growth in terms of users.

QGIS is regularly improved with many new features to better meet the needs of users. This is accomplished through the integration of a wide range of extensions in geographic information science, e.g., GDAL, GRASS, SAGA, Orfeo ToolBox (OTB), etc. as well as the development of its own QGIS Server, and a real Pythonbased script engine.

This set of four books describes, in the first volume, the operating principle of QGIS and the fundamental libraries most frequently used in image processing and geomatics: GDAL, GRASS, SAGA and OTB. This volume presents numerous core functionalities that will be implemented in several practical cases of remote sensing and spatial analysis presented in the other three volumes of the set: management and processing of raster and vector formats, georeferencing, geoprocessing tools, statistical analysis, spatial analysis (on networks, on surfaces) and classifications, starting from core processing up to visualization and cartographic editing.

Volumes 2 to 4 are devoted entirely to the description of various applications that use spatialized data, mainly satellite images. Each chapter in the four volumes is structured into three parts: (1) description of the application context, (2) methodology, and (3) implementation in QGIS and its libraries. Each of these volumes has a particular thematic flavor. Volume 2 is dedicated to applications in agriculture and forestry Volume 3 includes applications related to land use planning, whereas Volume 4 deals with applications covering water and risk management issues.

The use of GIS is becoming a fundamental tool for the scientific community and the public authorities responsible for the implementation, monitoring and evaluation of public policies. Indeed, GIS have evolved tremendously from systems originally planned for the visualization or representation of spatialized information, and the analysis of maps and related products, to more complete and versatile systems containing the most common tools for image processing and spatial analysis. Nowadays, GIS not only allow us to highlight the research results or an application project, but also to carry out the different stages of creation of the information and the knowledge necessary for these projects. QGIS, through its free and multiplatform philosophy, is a fertile breeding ground for these developments. It is even more so with the new paradigm in remote sensing: today, access to geospatial imagery is facilitated for a large number of actors; the cornerstone of studies, projects and research is becoming the capacity to process this large amount of data.

Consequently, the needs of the user community for teaching materials are very strong and we hope, through the publication of this set of books, to help facilitate the adoption of QGIS for beginners and to help those who already have some previous experience in the use of QGIS and its libraries to broaden their expertise.

Chapter 1 of this volume provides an introduction to QGIS. Four other Chapters (2, 3, 4 and 5) are devoted to the description of different libraries. Chapter 2 presents the GDAL library and its main functionalities, followed by Chapter 3 on GRASS, and Chapter 4 dedicated to SAGA, presenting their main visualization and processing tools. Chapter 5 is devoted to the OTB, mainly oriented toward image processing. Chapter 6 describes the use of Lizmap for the dissemination of an online land-use map, and Chapter 7 describes the two GeoHealth and QuickOSM extensions for health applications.

This work, carried out by scientists of a high technical level, is addressed to students (masters, engineering schools, PhD), engineers and researchers who have already adopted GIS. In addition to the texts of the proposed chapters, readers will have access to the data and tools allowing the complete realization of the scientific procedure described in each chapter, as well as access to screenshots of all the windows illustrating each step necessary to the realization of each application. Through this educational work, we hope to contribute to the appropriation of this tool for remote sensing purposes.

A supplement to the chapters, including databases and screenshots illustrating the practical application of the chapters, is available at the following address:

Using Internet Explorer: ftp://193.49.41.230

Using a FileZilla client: 193.49.41.230

Username: vol1_en

Password: 1loe34Nv@

We would like to thank everyone who contributed to the preparation of this book, first of all the authors of the chapters of course, but also the experts of the reading committee for their feedback on the chapters, the exercises, and the corrections made. This project was carried out thanks to the support of IRSTEA (French National Research Institute of Science and Technology for the Environment and Agriculture), CNRS (French National Center for Scientific Research), IGN (National Institute of Geographic and Forest Information) and CNES (French National Center for Space Studies).

We are very grateful to Airbus Defense and Space, CNES and Equipex Geosud for providing us with SPOT 5/6/7 images. Please note that these images may only be used for research and training purposes. Any commercial activity from the data provided is strictly prohibited.

Our thanks also go to our families for their encouragement and to André Mariotti (Professor Emeritus, Pierre and Marie Curie University) and Pierrick Givone (President, IRSTEA) for their encouragement and support for the realization of this project.

Nicolas BAGHDADI

Clément MALLET

Mehrez ZRIBI

1

Introduction to QGIS

1.1. History

QGIS (formerly known as Quantum GIS) is a free, open-source, cross-platform and scalable GIS tool with plugin development in Python and C++ languages. This is one of the official projects of the Open Source Geospatial Foundation (OSGeo, www.osgeo.org), whose mission is to help and promote the collaborative development of open-source geomatics software.

Today QGIS is a geographic information processing software suite that is popular with many users (www.qgis.org). Friendly and ergonomic, it makes it possible to collect, store, process, analyze, manage and present all types of spatial and geographic data similarly to the most highly priced software.

Initiated by Gary Sherman in 2002, QGIS was originally intended to be a data visualization tool for Geographic Resources Analysis Support System (GRASS) and PostGIS (Geographic Database Management System). It became a project of the OSGeo Foundation in 2007. The first major version 1.0 was released in 2009, version 2.0 in 2013 and version 3.0 is expected by the end of 2017. Supported by a community of developers structured into project committees, QGIS maintains a steady pace of integration of new features, resulting in a new minor release every 4 months (the most recent version is 2.18, version 3.0 is expected for 8 December 2017). In addition, the constant enrichment of the plugin library allows users to continuously benefit from new functionalities for customized uses and treatments.

The development of QGIS has been made with the contributions of a community of developers, translators and anomaly reporters who generally work on a voluntary basis but in some cases are professionals of an institution wishing to contribute to the project. A project steering committee ensures cohesion, the orientations of the project and the federation of the community.

Development is assured by a multitude of contributors, each competent in their field, forming a global QGIS community. There were 112 in the world in May 2016 at the time of the 15th international meeting of developers of QGIS in Girona. The management of contributions, exchanges with users and the diffusion of up-to-date news on the project can take place thanks to QGIS community spaces: websites, wikis, forums, mailing lists and the blog portal of the Frenchspeaking user group: http://osgeo.asso.fr/content/project/qgis-user-fr.

Technically, QGIS integrates the Geospatial Data Abstraction Library (GDAL), which allows it to read and process a large number of geographic images (free and proprietary). QGIS also supports a variety of vector data formats (PostgreSQL-PostGIS, Shapefiles, GPX, GeoJSON, SQLite, KML, MapInfo, Autocad DXF, ESRI Personal Geodatabase, Oracle Spatial, Erdas, ENVI, MBTiles, etc.). Other processing libraries such as Sextante are also integrated into QGIS.

Distributed under the GNU/GPL (General Public License) version 2, QGIS allows free access to a powerful, inexpensive GIS program that can be used on most platforms: GNU/Linux, Unix, Mac OS X and Windows.

1.2. QGIS graphical user interface

The QGIS graphical user interface (GUI) is presented below with, as illustrative data, the ROUTE 120® database available in open licensing on the site of the French National Geographic Institute (IGN): http://professionnels.ign.fr/route120.

1.2.1. Standard interface

As a standard, the interface presents (Figure 1.1):

– the Map View;

– the Browser, Layers and Overview Panel in the left panel;

– toolbars containing tools grouped by functionality around the map;

– the Status Bar with cursor coordinates, the coordinate system, scale, etc., at the bottom of the screen.

Figure 1.1. Standard QGIS GUI (v2.16) with ROUTE 120® database

1.2.2. Settings

The pre-setup of QGIS is done using the basic options of the software accessible via the Settings menu> Options (Figure 1.2).

The various tabs allow you to configure:

– General: the default options;

– CRS: the definition of the coordinate system;

– Networks: network and proxy settings for Internet access.

Figure 1.2. Settings: Options menu

1.2.3. Add layer

Adding layers is done using the Manage Layers toolbar buttons depending on the layer type (Figure 1.3).

Figure 1.3. Manage Layers toolbar

1.2.4. QGIS project

The QGIS working environment is saved in a project materialized by a file with the extension .qgs.

The information contained are as follows:

– open layers with links to access them;

– thematic analyses;

– the requests made;

– the semiology (style) of the layers;

– the projection used;

– zoom;

– completed layouts (maps);

– etc.

Since data are not contained in the project (Figure 1.4), care must be taken to preserve the access paths to the project when moving or transferring files.

Figure 1.4. Toolbar project

1.2.5. Navigation

The Map Navigation toolbar allows you to move and adjust the zoom of the screen (Figure 1.5).

Figure 1.5. Map Navigation toolbar

1.2.6. Attributes of entities

The Attributes toolbar allows you to select the entities, access and query the attribute data (Figure 1.6).

Figure 1.6. Attributes toolbar

1.3. The processing module, the toolkit for spatial analysis

1.3.1. History and interest of the treatment module

Since the earliest versions, QGIS software has provided spatial processing and analysis functions. But until version 1.8, these functions were only accessible via the drop-down menus and buttons of the main interface of the software. This only allowed the functions to be used in a graphic mode. It was therefore impossible to repeat one or more operations without laboriously reworking them with the interface.

In addition, since the QGIS software was designed in a modular architecture, many functions were available via additional extensions that users install according to their own needs. The disadvantage was that the various processing functions were dispersed in the menus of the different extensions. For the user, it was not always very intuitive in the interface to find the various useful tools, a chain of treatments requiring the use of very different